Fail `execute remote` early if the provided JWT secret is incorrect

Found another potential improvement:
If the Engine API's JWT secret is incorrect, `execute remote` starts failing all tests one by one, instead of failing early in `pytest_config`. We could do an early call to the Engine endpoint to check if the provided JWT secret is incorrect and exit early if that's the case.

We only need to implement some endpoint that does not have any effect in the client for this to work (perhaps this? https://github.com/ethereum/execution-apis/blob/main/src/engine/identification.md#engine_getclientversionv1).

I'll create an issue for this.

_Originally posted by @marioevz in https://github.com/ethereum/execution-spec-tests/issues/2084#issuecomment-3243303173_